In industrial countries, 36 to 128 per 100,000 inhabitants per year experience a sudden out-of-hospital cardiac arrest (“OHCA”) with survival remaining a rare event. Cardiovascular disease affects an estimated 80,700,000 North American adults, with approximately 2400 individuals dying from cardiovascular disease daily (an average of one death every 37 seconds). Approximately 310,000 coronary heart disease deaths due to OHCA occur annually.
According to data reported by the National Registry of Cardiopulmonary Resuscitation in 2007, over 75% of patients having cardiopulmonary arrest events did not survive the event. For those who did survive the event, an additional 35.2% died afterward.
In the 1950s, moderate hypothermia (body temperature of approximately 28° C. to approximately 32° C.) and deep hypothermia (body temperature of approximately <28° C.) were utilized for various surgical procedures as well as experimentally to reverse neurological insults associated with cardiac arrest. However, because of the numerous complications of moderate-to-deep hypothermia and the difficulty in inducing these temperature reductions, enthusiasm for the use of therapeutic hypothermia waned. Consequently, the use of hypothermia to help reverse the neurologic insult after normothermic cardiac arrest lay dormant for several decades. However, beginning in the late 1980s, positive outcomes following cardiac arrest were reported in dogs with mild hypothermia.
Contemporary use of mild therapeutic hypothermia following cardiac arrest in human patients is supported by recent randomized control trials and a meta-analysis of individual patient data. Major organizations, including the International Liaison Committee on Resuscitation (“ILCOR”) and the American Heart Association (“ANA”), recommend the induction of mild therapeutic hypothermia for comatose cardiac arrest survivors. However, the AHA therapeutic hypothermia guidelines lack a concrete description of exactly how to cool patients.
Despite widespread support for mild therapeutic hypothermia in the context of cardiac arrest, including consensus recommendations from major resuscitative organizations, the use of mild therapeutic hypothermia in clinical practice remains low. Many clinicians report that therapeutic hypothermia is too technically difficult to achieve in practice.
In addition, health care professionals occasionally need to induce hypothermia during certain surgical procedures or prevent inadvertent hypothermia and the multiple adverse effects that result from uncontrolled and unintended deviations from normal body temperature.
Control of a patient's body temperature while undergoing surgical procedures in the operating room is beneficial because, for instance, even mild inadvertent hypothermia during operative procedures increases the incidence of wound infection, prolongs hospitalization, increases the incidence of morbid cardiac events and ventricular tachycardia, and impairs coagulation.
Even mild hypothermia (<1° C.) significantly increases blood loss by approximately 16% and increases the relative risk for transfusion by approximately 22%, while maintaining perioperative normothermia reduces blood loss and transfusion requirement by clinically important amounts.
Because considerable strong evidence shows that thermal management improves outcomes in a variety of surgical patients, the current American Heart Association-American College of Cardiology 2007 Guidelines on Perioperative Cardiovascular Evaluation and Care for Noncardiac Surgery include a Level 1 recommendation for maintenance of perioperative normothermia.
Moreover, recognizing the numerous complications of perioperative hypothermia, the American Society of Anesthesiologists (ASA) has recently recommended that postoperative temperature become a basis for assessing physician compliance with current guidelines on the prevention of hypothermia.
Although inadvertent operative hypothermia is considered one of the most preventable surgical complications, existing methods to control body temperature are limited in efficacy, such that the incidence of inadvertent operative hypothermia for surgical patients can exceed 50%.
Currently available methods to control body temperature include both non-invasive and invasive techniques. For example, the most commonly used techniques developed to induce therapeutic hypothermia include surface cooling and invasive cooling.
Surface cooling is relatively simple to use, and can be accomplished by the use of external vests, cooling helmets, circulating cold-water blankets, cold forced-air blankets, or with less sophisticated methods, such as ice packs and cold-water immersion, but takes between 2 and 8 hours to reduce core body temperature. Surface cooling is limited by the rate at which cooling can occur, due to the tendency of blood flow to be shunted away from skin and towards the core. External devices, such as vests or blankets, significantly limit access to important patient areas that are often needed in critical care, such as for catheter placement, and require removal or modification to perform CPR. Surface cooling techniques such as ice packs limit the precision with which a patient's temperature can be controlled. Cooling with ice packs and conventional cooling blankets often results in unintentional overcooling.
For successful induction and maintenance of induced hypothermia and maintenance of normothermia, shivering, as well as other thermoregulatory responses, must be addressed. Benefits from cooling may be offset by negative consequences from shivering. Both pharmacological and nonpharmacological methods have been used to control shivering in therapeutic hypothermia, with meperidine offering one pharmacologic choice that may provide the greatest reduction in the shivering threshold, and other effective pharmacological agents being dexmedetomidine, midazolam, fentanyl, ondansetron, and magnesium sulfate. As a last resort, neuromuscular blocking agents are considered appropriate therapy for management of refractory shivering. Skin counterwarming techniques, such as use of an air-circulating blanket, are non-pharmacological methods for reducing shivering when used in conjunction with medication. Nevertheless, treatment for shivering while avoiding the negative consequences of many anti-shivering therapies is often difficult.
As another example, several methods are utilized to warm a patient, and include raising the operating room temperature and using external warming devices, such as forced-air warming blankets.
Several issues exist with these current methods: (1) excessively warm room temperature creates an uncomfortable environment for the surgical team, (2) forced-air warmers are bulky and may impact the surgical field; they tend to be inefficient and must be used for extended periods of time in the operating room, and (3) none of these systems adequately control or manage temperature, leading to both overheating or, more often, inadequate warming.
Rasmussen et al. (Forced-air surface warming versus oesophageal heat exchanger in the prevention of perioperative hypothermia. Acta Anaesthesiol Scand. 1998 March; 42(3):348-52) mention that forced-air warming of the upper part of the body is effective in maintaining normothermia in patients undergoing abdominal surgery of at least 2 h expected duration, while central heating with an esophageal heat exchanger does not suffice to prevent hypothermia. Brauer et al. (Oesophageal heat exchanger in the prevention of perioperative hypothermia. Acta Anaesthesiol Scand. 1998 March; 42(10):1232-33) states that an esophageal heat exchanger can only add a small amount of heat to the overall heat balance of the body.
Invasive temperature management treatments include: the infusion of cold intravenous fluids; the infusion of warmed intravenous fluids; cold carotid infusions; single carotid artery perfusion with extracorporeal cooled blood; cardiopulmonary bypass; ice water nasal lavage; cold peritoneal lavage; nasogastric and rectal lavage; and the placement of invasive intravenous catheters connected to refrigerant or heat exchange (warming) devices. Invasive temperature management treatments often require significant personnel involvement and attention to perform successfully. Moreover, certain invasive temperature management modalities have been associated with overcooling, overheating, or, more often, inadequate warming.
The use of intravenous fluid as a temperature management modality has the undesirable effect of contributing to circulating fluid volume overload, and has been found to be insufficient for maintaining target temperature. In addition, large volumes of fluids must be infused to obtain a significant effect.
Other techniques for achieving hypothermia include blood cooling through inhaled gases and the use of balloon catheters.
However, Andrews et al. (Randomized controlled trial of effects of the airflow through the upper respiratory tract of intubated brain-injured patients on brain temperature and selective brain cooling. Br. J. Anaesthesia. 2005; 94(3):330-335) mention that a flow of humidified air at room temperature through the upper respiratory tracts of intubated brain-injured patients did not produce clinically relevant or statistically significant reductions in brain temperature.
Dohi et al. (Positive selective brain cooling method: a novel, simple, and selective nasopharyngeal brain cooling method. Acta Neurochirgurgica. 2006; 96:409-412) mention that a Foley balloon catheter inserted to direct chilled air into the nasal cavity, when used in combination with head cooling by electric fans, was found to selectively reduce brain temperature.
Holt et al. (General hypothermia with intragastric cooling. Surg. Gynecol Obstet. 1958; 107(2):251-54; General hypothermia with intragastric cooling: a further study. Surg Forum. 1958; 9:287-91) mention using an intragastric balloon in combination with thermic blankets to produce hypothermia in patients undergoing surgical procedures.
Likewise, Barnard (Hypothermia: a method of intragastric cooling. Br. J. Surg. 1956; 44(185):296-98) mentions using an intragastric balloon for inducing hypothermia by intragastric cooling.
US Patent Application Publication 2004/0199229 to Lasheras mentions heating or cooling via a balloon inserted into a patient's colon.
US Patent Application Publication 2004/0210281 to Dzeng et al. (now U.S. Pat. No. 7,758,623) mentions a transesophageal balloon catheter for specifically cooling the heart and disparages technologies that cool the entire body.
US Patent Application Publication 2007/0055328 to Mayse et al. mentions a balloon catheter for protecting the digestive tract of a person undergoing cardiac ablation to correct cardiac arrhythmia. Mayse depicts an esophageal probe with a balloon that fits within the esophagus of a human body for the purpose of protecting the anterior wall of the esophagus from thermal injury that may occur during thermal ablation of the left atrium of the heart. The coolant that fills and circulates through the balloon maintains the temperature of the anterior wall of the esophagus within physiologically normal temperature ranges and thus prevents esophageal injury.
U.S. Pat. No. 6,607,517 to Dae et al. is generally directed to using endovascular cooling to treat congestive heart failure.
Several complications are known to result from increasing pressure within the gastrointestinal tract, as may occur with a balloon inflated within the stomach, colon, or other gastrointestinal organ. For example, stomach inflation may trigger intestinal rupture, regurgitation and aspiration that may result in pneumonia, esophageal tears, colon necrosis, and gut ischemia.
In addition, several temperature-controlling modalities, particularly those that employ inflatable balloons, limit access of the health care provider to particular anatomical structures that may be crucial for patient care, such as the stomach. These modalities may require removal or modification to achieve proper treatment.
To date, no available modality for controlling patient temperature has been found that sufficiently overcomes the technical, logistical, and financial barriers that exist. The ideal patient temperature control device has yet to be developed.
In summary, the state of the art related to the control of patient temperature comprises at least one significant long felt need: methods and devices for efficient, safe, and rapid control of patient temperature while maintaining access to anatomical areas necessary for additional treatment. The present technology identifies several indications, diseases, disorders, and conditions that can be treated or prevented by controlling patient temperature and, further, provides relatively non-invasive methods and devices for rapidly and efficiently controlling patient temperature while reducing the risks posed by prior devices and methods. Moreover, certain embodiments of the present technology provide relatively non-invasive methods and devices for rapidly and efficiently controlling patient temperature, while at the same time maintaining access to important anatomical structures. Certain embodiments of the present technology also provide methods and devices for inducing and maintaining mild hypothermia or maintaining normothermia in a subject without producing thermoregulatory shivering. Certain embodiments of the present technology also provide methods and devices for maintaining a subject's core body temperature within a narrow range with little variation around the goal temperature throughout the steady-state of the treatment protocol. Certain embodiments of the present technology also provide methods and devices for efficiently re-warming a subject following induced hypothermia.